R. L. WILLISTON July 29,1958DISTILLATION OF CYCLOHEXANONE FROM MIXTURES CONTAINING2,845,384. CYCLOHEXANONE, CYCLOHEXANOL, AND WATER Filed March 12, 1956

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AORNEY 2,845,384 United States Patent Office Patented July 29, 1958 2 An object of the present invention is to provide a con tinuous process for separating cyclohexanone in high 2,845,384 yield and purify from crude, wet cyclohexanone contain DISTILLATION OF CYCLOHEXANONE FROM ing cyclohexanol. Another object of the invention is to MXTURES CONTAINING CYCLOHEXA provide a continuous distillation process for purifying NONE, CYCLOHEXANOL, AND WATER and separating cyclohexanone from crude, wet cyclo Robert L. Williston, Kenmore, N. Y., assignor to Allied hexanone containing cyclohexanol which is efficient in Chemical Corporationa, New York, N. Y., a corpora operation and economical in construction. Other ob tion of New York jects and advantages will be apparent from the following 10 description and accompanying drawing. Application March 12, 1956, Serial No. 570,891 In accordance with the process of the present invention 4 Claims. (Cl. 202-42) cyclohexanone in high yield and purity may be separated from crude, wet cyclohexanone containing cyclohexanol in a continuous operation by continuously feeding a The invention relates to cyclohexanone and more par 15 stream of crude, wet cyclohexanone into a fractionating ticularly refers to a new and improved process for con column, continuously introducing cyclohexene into said tinuously separating cyclohexanone from mixtures con fractionating column, continuously removing as vapor taining it together with water and cyclohexanol to obtain from the top of the fractionating column as azeotrope a cyclohexanone product of high purity. composed of water and cyclohexene, continuously condens Cyclohexanone is commercially produced by vapor 20 ing said vapor azeotrope, continuously separating said con phase dehydrogenation of cyclohexanol at elevated tem densate into an aqueous phase and an oil phase containing peratures over a zinc-copper catalyst. The crude product cyclohexene, returning cyclohexene from the oil phase to thus obtained usually contains over 90% of cyclohexanone the fractionating column, continuously withdrawing de and less than about 10% of impurities, notably cyclo hydrated cyclohexanone containing cyclohexanol from the hexanol and water, as well as small amounts of phenol 25 bottom of the fractionating column, continuously passing and by-product hydrocarbons such as cyclohexene. said dehydrated cyclohexanone-cyclohexanol to a second Under ordinary pressure cyclohexanone and cyclo fractionating column maintained at an absolute pressure hexanol boil within 5 of each other (155° C. and 160° C. below 100 mm. Hg, continuously removing cyclohexanone respectively), and hence cannot be readily separated by vapor of high purity from the top of said second frac distillation. However, under reduced pressures of less 30 tionating column, continuously condensing and collecting than 100 mm. Hg abs. these compounds possess suffi said pure cyclohexanone and continuously withdrawing ciently different volatilities, i. e. more widely different cyclohexanol as bottoms from the bottom of the second boiling points such as to permit fractional distillation. fractionating column. Water, as a component of the mixtures of cyclohexanone Referring to the drawing, the feed to the continuous and cyclohexanol, complicates the situation in that water 35 distillation system entering through line 1 is crude, wet forms azeotropes with both cyclohexanone and cyclohex cyclohexanone which may be produced by dehydrogen anol, which possess very close boiling points (96. C. and ation of cyclohexanol and is a mixture of 80-90% or 98 C. respectively, at 760 mm. Hg abs.). Consequently, more of cyclohexanone, usually about 5-10% cyclohex in view of the small difference in boiling points of these anol and about 0.5-3% water together with small azeotropes, these substances cannot be readily separated 40 amounts of other impurities such as phenols, polymers by distillation as long as water is present in mixture there and hydrocarbons. In crude cyclohexanone produced by with and it is necessary to remove water from the mixture hydrogenation of phenol followed by dehydrogenation prior to separation of the cyclohexanone in order to of resultant cyclohexanol the resultant crude product con prevent contamination of the cyclohexanone with tains about 1-2% cyclohexene as an impurity. Fraction cyclohexanol. 45 ating column 2, into which feed enters through line 1, Crude, wet cyclohexanone containing cyclohexanol and may be any suitable fractionating tower, preferably a col small amounts of other impurities may be distilled in a umn of the bubble cap type. Heat is provided in the bot batch operation by first removing a forerun containing tom of fractionating column 2 by means of steam coil 3 the Water, hydrocarbon and other impurities which are or alternatively, not shown in the drawing, a convention separately collected and then fractionally distilling the 50 al reboiler section. Fractionating column 2 is preferably residue in vacuo to separate the cyclohexanone. While operated at about atmospheric pressure, but may, although the batch distillation is satisfactory for the separation of not a preferred method of operation, be operated at su small amounts of cyclohexanone, for large volume opera per-atmospheric or sub-atmospheric pressures. Cyclo tions, a continuous distillation process is more desirable hexene from an external source entering through line 4, and economical. 55 or recycled cyclohexene entering through line 5, is intro A continuous distillation process for purifying crude duced through line 6 into fractionating column 2 where cyclohexanone has been suggested wherein a stream of in it forms an azeotrope, with the water entering with the crude cyclohexanone is introduced into a fractionating feed through line 1. This azeotrope, which boils at 70.8 column, the water removed as overhead in the form of C. at 760 mm. Hg abs. and contains about nine parts cyclohexanone-water and cyclohexanol-water azeotropes, 60 by weight of cyclohexene per part of water, is removed while dehydrated, crude cyclohexanone is removed as as overhead through line 7, condensed in water-cooled bottoms. The overhead is condensed and stratified into condenser 8 and the condensate then passes down through two layers: The upper layer poor in water is returned to lines 9 and 11 into receiver 12 wherein the condensate the first column, while the lower layer rich in water is collects and separates into a lower aqueous layer 13 and introduced into a second column for removal of water. 65 an upper oily layer 14 containing cylohexene. Non-con This involves the use of two continuous fractionation densible gases and vapors are released from the top of columns with their attendant accessories and requires re receiver 12 through line 15 and valve 16 and may be dis cycling two wet fractions to the first column with increased charged to the atmosphere. The water from the phase formation of auto-condensation products due to long resi separation, being virtually free from cyclohexene and dence time. The dry, crude cyclohexanone from the first 70 other organic components, may be discarded through column is fractionated in a third column to remove cyclo line 17 to sewer. A portion of the condensate flowing hexanol and other high boiling impurities. down through line 9 may be returned to the top of frac 2,845,384 3 4. tionating column 2 via line 18 and valve 19 to cool the cyclohexanol, 1.4% cyclohexene, 0.5% water, 0.1% top of the fractionating column and maintain it at the phenol and 0.5% condensation products-was fed into proper temperature. The total amount of cyclohexene a 30 plate commercial bubble cap column at approxi introduced into column 2 as added cyclohexene enter mately the 15th plate. Sufficient cyclohexene was fed ing through line 4, or recycled cyclohexene entering into the column at approximately the 15th plate to main through line 5, or as an impurity in the crude cyclohex tain the head temperature at 70.5-71. C. at 760 mm. anone feed entering through line 1, should be sufficient Hg abs. This quantity is normally about 101 lbs./hr. to provide equilibrium conditions, viz. to remove essen and must be sufficient to give a total of 9 parts by weight tially all of the water present in the crude, wet cyclohex of cyclohexene for each part of water in the feed. The anone feed as a cyclohexene-water azeotrope. If an in 10 column overhead with a rate of approximately 300 lbs./hr. sufficient amount of cyclohexene is introduced for a sub was condensed in a suitable condenser, from which half stantial length of time the cyclohexanone bottoms will of the condensate was returned to the top of the column contain an increased concentration of water. The pres as reflux while the other half was run to a phase sepa ence of water in the bottoms when subsequently fraction rator, wherein it was automatically separated into a cyclo ated in the second column to separate cyclohexanone hexene layer and a water layer. A portion of the cyclo from cyclohexanol will cause cyclohexanol to distill over hexene layer, approximately 101 lbs./hr., was recycled and contaminate the cyclohexanone product due to the to the column, the remainder being drawn off to storage. formation of close-boiling azeotropes of these substances The water from the separator, equivalent to about 16 with water. Conversely, if substantially more cyclohex lbs./hr. and containing less than 0.1% organic com ene is employed than is required to azeotrope the water, 20 pounds, was discarded to the sewer. Sufficient heat was the excess will not be completely vaporized as overhead continuously fed to the reboiler located at the bottom and will tend to contaminate the cyclohexanone bottoms. of the column to maintain a temperature of 160-162 C. This in turn will result in contamination of the distilled The bottoms, containing all of the cyclohexanone, cyclo cyclohexanone product from the second column. Cyclo hexanol and higher boiling compounds of the feed and hexene need be supplied usually in the initial stages of 25 less than 0.02% cyclohexene or water, were continuously operation from an external source and introduced into withdrawn at a rate of approximately 3143 lbs./hr. the fractionating column through line 4 as shown in the The bottoms from the dehydration column were fed drawing. After equilibrium conditions are set up there continuously into a 60 plate bubble cap column main will be sufficient cyclohexene in layer 14 from which the tained at a head pressure of 50 mm. Hg abs. In this cyclohexene may be removed through line 21 and forced 30 second column cyclohexanone was removed overhead at by pump 22 through lines 5 and 6 into tower 2. Any ex a temperature of 76° C. while a residue rich in cyclo cess cyclohexene may be sent through line 23 to storage. hexanol was withdrawn as bottoms. The cyclohexanone The bottom of tower 2 is maintained at a temperature of product thus obtained was found on analysis to contain about 155-165 C. by means of steam coil 3 to provide more than 99.95% cyclohexanone, less than 0.02% of heat for distilling the azeotrope and to volatilize the water 35 water, cyclohexene or cyclohexanol and less than 50 and other volatile constituents from the cyclohexanone p.p.m. of phenol. cyclohexanol bottoms collecting in the bottom of tower . Although certain preferred embodiments of the inven 2. In this manner water can be completely removed in tion have been disclosed for purpose of illustration, it a single column instead of requiring two columns as in will be evident that various changes and modifications the prior art. In addition, this provides a superior proc 40 may be made therein without departing from the scope ess due to simplification of procedure and equipment and and spirit of the invention. reduction in amount of autocondensation by-products I claim: formed due to shorter exposure of the cyclohexanone to 1. A continuous process for separation and purifica elevated temperatures. - tion of cyclohexanone from cyclohexanone containing The dehydrated cyclohexene-free crude cyclohexanone 45 water and cyclohexanol as impurities which comprises cyclohexanol is continuously withdrawn from the bottom continuously feeding a stream of impure cyclohexanone of column 2 through line 24 and directed by pump 25 into a fractionating zone, continuously introducing cyclo into fractionating column 26, similar in construction to hexene into said fractionating zone to form an azeotrope column 2 except it is usually provided with a greater num with the water in said impure cyclohexanone, con ber of bubble cap plates. Heat may be supplied to the tinuously removing as vapor from the fractionating zone bottom of tower 6 by means of a steam coil. Fractionat the azeotrope composed of water and cyclohexene leav ing column 26 is operated under sub-atmospheric pressure ing dehydrated cyclohexanone containing cyclohexanol of below about 100 mm. Hg abs., preferably below about as bottoms in the fractionating zone, continuously con 50 mm. Hg abs. The temperature in column 26 will densing said vapor azeotrope, continuously withdrawing vary depending upon the pressure but generally will be 55 said dehydrated cyclohexanone containing cyclohexanol found to have a top temperature of about 70-90° C. and a bottom temperature of about 10 to 40 higher. Cyclo from the fractionating zone, passing said dehydrated hexanone vapors released from the top of column 26 cyclohexanone-cyclohexanol to a second fractionating through line 27 are condensed in condenser 28 and then Zone maintained at an absolute pressure below about 100 flow through line 29 into receiver 31. A portion of the 60 mm. Hg, continuously removing cyclohexanone vapor of cyclohexanone condensate collecting in receiver 31 is re high purity from said second fractionating zone leaving turned by pump 32 through line 33 for refluxing and cyclohexanol as bottoms in said second fractionating cooling into the top of tower 26. Vacuum is maintained Zone, continuously condensing and collecting said cyclo on the system through line 34 and valve 35 connected to hexanone of high purity, and continuously withdrawing the top of receiver 31. High purity cyclohexanone col cyclohexanol as bottoms from the second fractionating lecting in receiver 31 is sent through line 36 to storage. ????. The cyclohexanol bottoms collecting in fractionating col 2. A continuous process for separation and purifica umn 26 and heated by steam coil 37 are withdrawn and tion of cyclohexanone from cyclohexanone containing sent to storage through line 38. water and cyclohexanol as impurities which comprises The following example illustrates the present inven 70 continuously feeding a stream of impure cyclohexanone tion: into a fractionating zone, continuously introducing cyclo A stream of 3258 lbs./hr. of wet crude cyclohexanone, hexene into said fractionating zone to form an azeotrope which was obtained by dehydrogenation of cyclohexanol with the water in said impure cyclohexanone, continu vapors over a zinc-copper catalyst and which possessed ously removing as vapor from the fractionating zone the the following analysis: 92.2% cyclohexanone, 5.3% 75 azeotrope composed of water and cyclohexene leaving 2,845,384 5 6 - dehydrated cyclohexanone containing cyclohexanol as 4. A continuous process for separation and purificatio bottoms in the fractionating zone, continuously condens of cyclohexanone from cyclohexanone containing water ing said vapor azeotrope, continuously separating said and cyclohexanol as impurities which comprises con condensate into an aqueous phase and an oil phase con tinuously feeding a stream of impure cyclohexanone into taining cyclohexene, continuously returning cyclohexene a fractionating zone maintained under substantial atmos from the oil phase to the fractionating zone, continuously pheric pressure, continuously introducing cyclohexene withdrawing said dehydrated cyclohexanone containing into said fractionating zone to form an azeotrope with the cyclohexanol from the fractionating zone, passing said water in said impure cyclohexanone, continuously re dehydrated cyclohexanone-cyclohexanol to a second frac moving as vapor from the fractionating zone the azeo tionating Zone maintained at an absolute pressure below O trope composed of water and cyclohexene leaving de about 100 mm. Hg, continuously removing cyclohexa hydrated cyclohexanone containing cyclohexanol as bot none vapor of high purity from said second fractionating toms in the fractionating zone, continuously condensing Zone leaving cyclohexanol as bottoms in said second frac said vapor azeotrope, returning a portion of said con tionating Zone, continuously condensing and collecting densate to the fractionating zone to maintain the tem said cyclohexanone of high purity, and continuously with 15 perature of the vapor leaving the fractionating zone at drawing cyclohexanol as bottoms from the second frac about 71 C., continuously separating said condensate tionating Zone. into an aqueous phase and an oil phase containing cyclo 3. A continuous process for separation and purifica hexene, continuously returning cyclohexene from the oil tion of cyclohexanone from cyclohexanone containing phase to the fractionating zone in an amount sufficient water, cyclohexanol and a minor amount of cyclohexene 2. to maintain a proportion of about nine parts by weight which comprises continuously feeding a stream of impure of cyclohexene per part of water in the fractionating cyclohexanone into a fractionating zone, continuously zone, continuously withdrawing said dehydrated cyclo introducing cyclohexene into said fractionating zone to hexanone containing cyclohexanol from the fractionating form an azeotrope with the water in said impure cyclo zone, passing said dehydrated cyclohexanone-cyclohex hexanone, continuously removing as vapor from the frac 25 anol to a second fractionating zone maintained at an tionating zone the azeotrope composed of water and cyclo- . absolute pressure below about 100 mm. Hg, continuously hexene leaving dehydrated cyclohexanone containing removing cyclohexanone vapor of high purity from said cyclohexanol as bottoms in the fractionating zone, con second fractionating zone leaving cyclohexanol as bottoms tinuously condensing said vapor azeotrope, continuously in said second fractionating zone, continuously condensing separating said condensate into an aqueous phase and an 30 and collecting said cyclohexanone of high purity, con oil phase containing cyclohexene, continuously returning tinuously returning a portion of said condensate as reflux cyclohexene from the oil phase to the fractionating zone to said second fractionating zone, and continuously with in an amount sufficient to maintain a proportion of about drawing cyclohexanol as bottoms from the second frac nine parts by weight of cyclohexene per part of water in tionating zone. the fractionating zone, discharging excess oil phase con 35 taining cyclohexene from the system, continuously with References Cited in the file of this patent drawing said dehydrated cyclohexanone containing cyclo UNITED STATES PATENTS hexanol from the fractionating zone, passing said de hydrated cyclohexanone-cyclohexanol to a second frac 2,377,421 Frey ------June 5, 1945 tionating zone maintained at an absolute pressure below 40 2,552,911 Steitz ------May 15, 1951 about 100 mm. Hg, continuously removing cyclohexanone vapor of high purity from said second fractionating Zone OTHER REFERENCES leaving cyclohexanol as bottoms in said second fractionat “Azeotropic Data,” American Chemical Society, 1952. ing zone, continuously condensing and collecting said “Elements of Fractional Distillation,” Robinson and cyclohexanone of high purity, and continuously with 45 Gilliland, fourth edition, McGraw-Hill, 1950, chapter 10. drawing cyclohexanol as bottoms from the second frac “Technique of Organic Chemistry,” vol. 4; Distillation, tionating zone. Weissberger, chapter 3, Interscience 1950.